1. Field of the Invention
The present invention relates to an image display for displaying color images.
2. Description of the Related Art
Various types of displays have been developed for displaying color images, including the direct viewing and projection types. The direct viewing display uses a liquid crystal panel, plasma display panel (PDP), CRT or the like to display an image that the viewer views directly. The projection display is equipped with a projection lens, various optical systems and a display device such as a liquid crystal panel, digital micromirror device (DMD, trademark of Texas Instruments Inc.) or CRT. An image formed on the display device is projected onto a screen, for instance, for viewing.
Ideally, the image displayed by a color display is uniform, i.e., totally free of unevenness. Actually, however, unevenness sometimes arises in the displayed image for reasons that will now be discussed.
When a liquid crystal panel is used as the display device, image data are applied to the individual pixels of the liquid crystal panel to vary the transmittance and reflectance of the pixels with respect to illumination light projected onto the panel. The light projected onto the panel exits from the panel as image-bearing light. To ensure that images are displayed with no unevenness, the transmittance and reflectance characteristics of the liquid crystal should be the same at every pixel. In an actual liquid crystal panel, however, they vary to some extent. The color of the displayed image is therefore sometimes uneven. Color unevenness also occurs when other types of display devices are used, owing to non-uniformity of the various display device characteristics.
Display devices like the liquid crystal panel and the digital micromirror device require a separate optical system for projecting illumination light. Color unevenness may be produced in the displayed image depending on the luminance and color distribution of the light from the illumination optical system.
In the case of a projection display, color unevenness sometimes arises in the displayed image for reasons related to the characteristics of the display's various optical systems.